Refrigerants

# Refrigerants Notes | Study Thermodynamics - Mechanical Engineering

## Document Description: Refrigerants for Mechanical Engineering 2022 is part of Applications for Thermodynamics preparation. The notes and questions for Refrigerants have been prepared according to the Mechanical Engineering exam syllabus. Information about Refrigerants covers topics like and Refrigerants Example, for Mechanical Engineering 2022 Exam. Find important definitions, questions, notes, meanings, examples, exercises and tests below for Refrigerants.

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REFRIGERANTS

Compressors for Different Refrigerants

 Refrigerant Compressor NH3 Reciprocating & screw compressor R=11 Centrifugal compressor R-12 Reciprocating compressor R-22 Reciprocating compressor R-113 Centrifugal compressor R-114 Rotary compressor

Applications of Refrigerants

 Refrigerant Application NH3 Cold storage, ice plants, refrigerators H2O Water, Li Br absorption system CO2 Used as dry ice in transport R-11 Central air conditioning R-12 Domestic refrigerator, water cooler R-22 Window type air conditioner R-113 Air conditioning

DESIGNATION OF REFRIGERANTS
Saturated Hydrocarbons

•  If the compound is CmHnFpClq
n + p + q = 2m + 2

then,

designation is R(m - 1) (n + 1) P

Eg. CCI3 is R-11

•  The brominated refrigerants are denoted by and additional B and a member to denote as to how many chlorine atoms are replaced by bromine atoms

Eg. CF3 Br is R13 B1

Unsaturated Compounds - CmHnFpClq
where n + p + q = 2m
they are designated by R (m-1) (n+1)P
Eg. C2H4 is R1150

Inorganic Refrigerants
Designation is R (700 + molecular weight)
Eg. NH3 is R 717, CO2 is R744

Basic properties of Some important Refrigerants

CFC 12 or R-12-or CCl2F2

•  Normal boiling point (N.B.P.) = 29.8ºC
•  It is used in domestic refrigerators, car air conditioners, water coolers etc.
•  It is used with reciprocating compressor
•  Because of low value of g. discharge temperature is low. so it is very suitable for hermetically sealed units

CFC-11 or R-11 or CCl3F

•  N.B.P. -23.7ºC
•  Having more boiling point, It has vacuum in the evaporator.
•  It is used with centrifugal compressor.
•  Its application is in central air conditioning.

HCFC-22 or R-22 or CHClF2

•  N. B. P. – 40.8ºC
•  It is used in window air conditioning.
•  It is used with reciprocating compressor.
•  It has high g value, so discharge temperature is high. Thus it is not very suitable for hermetically sealed unit for more than one year.
•  N.B.P. of commercially used refrigerants vary from -50ºc to + 50ºC.

PROPERTIES OF GOOD REFRIGERANTS

•  Low boiling point
•  Evaporating pressure should be low and positive and near to atmospheric pressure
•  High critical temperature
•  Low critical pressure
•  Low freezing point
•  Non flammable, non explosive
•  Either completely miscible or completely immiscible with oil
•  Non corrosive
•  High dielectric strength
•  High thermal conductivity
•  Low viscosity
•  Low specific heat
•  Low surface tension
•  Low cost

SECONDARY REFRIGERANTS

•  They are used to reduce the quantity of main refrigerant and to reduce pressure losses. They are cheap in cost.

Eg. brines such as : CaCl+ Water & NaCl + water, Ethylene glycol + water and propylene glycol + water.

•  CaCl2 and NaCl is mixed with water to reduce the freezing point of water.

OZONE DEPLETION

•  Ozone layer is in stratosphere.
•  It protects humans from UV rays which can cause skin cancer.
•  Chlorine atoms in CFC causes ozone depletion.
•  Hydro-Chloro-flouro-carbons (HCFCs) have low ozone depletion tendency because of less chlorine.

But they have Global warming tendency.

• Pure hydro carbon is highly inflammable due to hydrogen atoms.
• Azerotrope: These are non ideal mixtures of two or more refrigerants behaving as pure substance having close N.B.P. Their bubble point temperature is equal to dew point temperature.
• Bubble temperature is the temperature at which liquid mixture starts boiling.
• Dew point temperature is the temperature at which vapour mixture starts condensing.
• CO2 refrigeration system has very low COP because critical temperature of CO2 is very low and very close to condensing temperature.
• Because of flammability & toxicity, ammonia is not used in domestic refrigerator, comfort air conditioning.
• If water content in refrigerant is more than that can be dissolved by the refrigerant, there is a danger of ice formation and consequently choking of capillary tube used in throttling system. This is moisture chocking.
• Silica gel is used in liquid line for dehydration of refrigerant.
• Miscibility of refrigerants with oil
 Refrigerant Miscibility with oil R-11, R-12 Good miscibility NH3, CO2 No miscibility R-22 Partial miscibility
•  In evaporator, oil separates from refrigerant vapour. Accumulation of oil in evaporator called oil choking.
•  In immiscible oil refrigerant mixture, oil separator is used after compressor.
•  Ammonia corrodes copper. So iron and steel are used with its system.
•  Refrigerants in decreasing order of normal boiling point.

R-11(–23.7ºC) > R-12(-290C) > NH3(–33.30C) > R-22(–410C) > CO2(– 73.60C)

• Refrigerants in increasing order of freezing point

CO2 < NH3 < R-11 < R-12 < R-22

• Refrigerants in decreasing order of critical temperature

R-11 < NH3 < R-12 < R-22 < CO2

• Refrigerants in decreasing order of Critical Pressure

NH3(113.86) > CO2(73.8) > R-22 > R-11 > R-12(41.2)

• Refrigerants in decreasing of COP

R -11 > NH3> R-12> R-22> CO2

Leakage Detection of Refrigerants

 Leakage Detected By NH3 Burning sulphur candle Halocarbon Halide torch test Hydrocarbon and Propane Soap and water test SO2 NH3 swab test Refrigeration electronic leak detector Equipment (high sensitivity)
The document Refrigerants Notes | Study Thermodynamics - Mechanical Engineering is a part of the Mechanical Engineering Course Thermodynamics.
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